For making electrical contact with and connecting up a semiconductor module, electrical connections are required which have to be led through the housing to the outer side of the housing. Through the corresponding bushings on the housing, water vapor and/or other substances can penetrate into the interior of the semiconductor module, which can lead to impairment of the elements situated in the module, for example as a result of corrosion. Although semiconductor modules are potted with silicone gels for various reasons, said gels do not constitute a particularly good barrier for water vapor or other harmful substances, and so the problem outlined is scarcely improved.
In further module designs, that region of the housing interior which is situated above the silicone gel is filled with a hard potting composed of epoxy resin that bears on the silicone gel. Although such modules are less permeable to gases and water vapor than modules which contain a silicone gel but no hard potting, the hard potting encloses the silicone gel together with the housing. Silicone gels have a high coefficient of cubical thermal expansion, which, in the event of the semiconductor module being subjected to high loads resulting from temperature cycles, can give rise to an excess pressure or a reduced pressure which can cause damage in the interior of a module. In the case of excess pressure in the gel, it is possible for gel to escape between baseplate and housing. In the case of reduced pressure, cracks can form in the gel. Apart from that, in the corresponding commercially available modules, the purpose of the additional hard potting is to mechanically stabilize components in the interior of the semiconductor module.